Defibrillation concepts

Question 1

What 3 things determine cardiac response to a shock?

Answer 1

1. Passive and active ion channel properties of cell membranes
2. Properties of electrical connections between cells
3. Effects on intracellular events such as calcium release

Question 2

A pacing stimulus affects what phase of the action potential?

Answer 2

Phase 4 (Diastole).

Question 3

A defibrillation stimulus affects what phase of the action potential?

Answer 3

Phase 2 (plateau) or Phase 3 (polarization).

Question 4

The following statement describes what phenomena?

‘Secondary sources of electrical potential in tissue sites remote from stim electrodes’.

Answer 4

Virtual electrode.

Question 5

The following statement describes the _____ period.

‘Portion of cardiac cycle’s relative refractory period where shocks can induce VF’.

Answer 5

Vulnerable Period.

Question 6

Shocks in vulnerable period induce VF if which 2 criteria are satisfied?

Answer 6

1. Energy is at or above VF threshold
2. Below upper limit of vulnerability

Question 7

The following statement best describes what?

‘Weakest shock strength where VF is not induced when shock is delivered during vulnerable period’.

Answer 7

Upper limit of vulnerability.

Looks like a rhombus on top of T-wave.

Question 8

What 3 theories define ‘Critical Point’?

Answer 8

1. Winfree
2. Efimov
3. DADs

Question 9

Define the mother rotor theory of VF.

Answer 9

Mother rotor is the central generator of wavefronts, which then split into daughter wavefronts.

Terminate the mother generator = terminate the rhythm.

Question 10

List two predominant programmable parameters that influence defib success.

Answer 10

1. Voltage
2. Waveform duration (Time constant of cardiac tissue)

Question 11

What is the benefit of waveform truncation?

Answer 11

Truncating the waveform = Improved success.

When compared to allowing the discharge to decay indefinitely. This has been demonstrated as pro-arrhythmic.

Question 12

Calculate waveform tilt.

Answer 12

1 minus (Trailing edge / Leading edge).

Question 13

Defib waveform tilt reprogramming is only available in which manufacturer?

Answer 13

Abbott.

Question 14

True or False:

Defibrillation Threshold = Leading Edge Voltage.

Answer 14

True

Question 15

What are most estimates of defibrillation membrane time constant?

Answer 15

2.5 - 4.5ms.

Question 16

What is the range of capacitance in today’s ICDs (Farads).

Answer 16

105-150 µF.

Question 17

True or False:

Cathodal shocks produce expanding, pro-arrhythmic wavefronts away from the physical cathode toward a virtual anode.

Answer 17

True

RV cathodal shock = post-shock virtual anodal electrodes = expanding pro-arrhythmic wavefronts.

Question 18

True or False:

Both appropriate and inappropriate shocks increase risk of mortality in HF patients.

Answer 18

True

5 fold risk increase with appropriate therapy

2 fold risk increase with inappropriate therapy

Question 19

What is the success rate of 1st shock therapy?

Answer 19

90%.

Question 20

Following ATP is shock efficacy increased or decreased?

Answer 20

Decreased to below 90%.

Thus program max shock energy following ATP.

Question 21

DFT is normally in what range (Joules)?

Answer 21

5-30J.

Question 22

List two major contraindications for DFT.

Answer 22

1. Severe Aortic Stenosis
2. Intra-cavity Thrombus

Question 23

When is the vulnerable period of the T-wave (as a % from onset)?

Answer 23

20-60% from T-wave onset.

Question 24

What is the DFT safety margin?

Answer 24

First therapy = 10J below max output.

Question 25

Define high DFT.

Answer 25

\<10J below max output. ## Footnote *Occurs in approximately 5% of patients.*

Question 26

What 5 considerations increase risk of high DFT?

Answer 26

1. Young age 2. Low EF 3. HCM 4. Medication (Amiodarone) 5. High Body Mass Index

Question 27

List 7 reversible causes of high DFT.

Answer 27

1. Hypotension 2. Pneumothorax 3. Effusion / Edema 4. Acidosis 5. Electrolyte imbalance 6. Medications 7. Ischemia

Question 28

Which two drugs reduce DFT?

Answer 28

1. Sotalol 2. Dofetilide

Question 29

List three programmable ways to reduce a high DFT.

Answer 29

1. Program from RV Anode (Normal) to RV Cathode (maybe pro-arrhythmic) 2. Vector change (Include SVC coil Waveform) 3. Change tilt (Abbott)

Question 30

List three invasive ways to reduce a high DFT.

Answer 30

1. Reposition to lead to apical position 2. Implant Subcutaneous array or CS / Azygous Vein defibrillation leads 3. Upgrade to high output device

Question 31

List two conditions that should be met before programming alterations to defib waveform.

Answer 31

1. High DFT 2. High HV impedance

Question 32

At what % of capacitor discharge is a biphasic shock commonly interrupted?

Answer 32

65% of capacitor discharge.

Question 33

What does Upper Limit of Vulnerability predict?

Answer 33

Defibrillation energy that has a 90% chance of success.

Question 34

The following statement best describes what? 'Lowest shock energy delivered on vulnerable period which does not induce VF'.

Answer 34

Upper limit of Vulnerability.

Question 35

What are two major advantages of ULV testing vs DFT testing?

Answer 35

1. Ability to predict DFT without inducing VF 2. Reproducibility superior to DFT testing

Question 36

List three major limitations of ULV testing vs DFT.

Answer 36

1. Indirect measurement - less accurate 2. Doesn't confirm device's ability to detect arrhythmia like DFT 3. Multiple shocks required at different coupling intervals - mortality of many shocks potentially worse than DFT

Question 37

List 4 benefits of S-ICD vs ICD.

Answer 37

1. No vascular injury 2. No systemic infection 3. No Fluoro required 4. Less invasive

Question 38

List 2 limitations of S-ICD vs ICD.

Answer 38

1. Lack of ATP 2. Lack of Brady therapy

Question 39

What are the 3 sensing vectors of S-ICD?

Answer 39

1. Primary = B (suprasternal) to can 2. Secondary = A( sternal notch) to can 3. Alternate = Sternal notch to Suprasternal

Question 40

What 3 algorithms work in sync in S-ICD systems?

Answer 40

1. Static morphology - compares to sinus rhythm template 2. Dynamic morphology - compares polymorphic rhythms by beat to beat comparison 3. QRS width analysis - compares to sinus rhythm template

Question 41

How many shocks will an S-ICD deliver and at what output?

Answer 41

5 x 80J

Question 42

Which two studies investigate S-ICD performance?

Answer 42

1. IDE = Cornerstone for FDA approval 2. EFFORTLESS = Investigates long term follow-up

Question 43

What is the complication free rate of S-ICD for IDE and EFFORTLESS?

Answer 43

IDE = 92% EFFORTLESS = 94%

Question 44

What is the first shock efficacy rate of S-ICD for IDE and EFFORTLESS?

Answer 44

IDE = 94.7% EFFORTLESS = 99.7%

Question 45

Which RA position reduces likelihood of FFRWS?

Answer 45

Lateral Free wall.

Question 46

What is a typical leading edge shock voltage range?

Answer 46

750-900V.

Question 47

# True or False: Biphasic shocks reduce DFT by 30-40% vs Monophasic shocks.

Answer 47

True

Question 48

Waveform tilt is normally at what percentage?

Answer 48

50%.

Question 49

# True or False: Voltage stored on the capacitor is equal to initial shock waveform.

Answer 49

True

Question 50

# True or False: Current thinking predominantly favours the Mother Rotor theory of VF.

Answer 50

False ## Footnote *This theory has fallen out of favour recently.*

Question 51

# True or False: Shock waveform truncation is pro-arrhythmic vs. non-truncated delivery.

Answer 51

False ## Footnote *Truncated waveforms are less likely to induce arrhythmia.*

Question 52

Shocks are predominantly bi-phasic. What is the primary purpose of the 1st phase?

Answer 52

Primary purpose of 1st phase of biphasic shock is to maximise voltage change in the cardiac cell membrane.

Question 53

Shocks are predominantly bi-phasic. What is the primary purpose of the 2nd phase?

Answer 53

Primary purpose of 2nd phase is to discharge cardiac membrane potential back to 0V. ## Footnote *Effectively removing charge from the 1st phase.*

Question 54

The following statement best describes what? 'Beneficial effect of phase 2 is maximal when it completely removes the charge delivered by phase 1'.

Answer 54

Charge Burping / Charge Balancing.

Question 55

Is charge burping less or more likely to induce arrhythmia?

Answer 55

Less. ## Footnote *The point is to absorb initial energy and return membrane to 0mV. Thus charge burping is less arrhythmogenic.*

Question 56

# True or False: Post shock virtual electrodes launch new wavefronts towards the physical shock anode.

Answer 56

True

Question 57

# True or False: Anodal shocks produce expanding, pro-arrhythmic wavefronts away from the physical cathode toward a virtual cathode.

Answer 57

False ## Footnote *RV anodal shock = post-shock virtual cathodal electrodes = collapsing, self- extinguishing wavefronts*

Question 58

# True or False: With regards to shock electrode programming. 'RV cathode produces expanding, proarrhythmic wavefronts, whereas a RV anode produces collapsing, self-extinguishing wavefronts'.

Answer 58

True ## Footnote *RV Cathode is demonstrably more proarrhythmic.*

Question 59

ICD charge delivered is the relationship between \_\_\_\_\_\_\_.

Answer 59

Initial voltage vs. final voltage on capacitor.

Question 60

# Parallel / Series How are capacitors charged and discharged?

Answer 60

Charged in **parallel** Discharged in **series**

Question 61

How do DR ICD leads help prevent far field ventricular over sensing?

Answer 61

Short intra-electrode spacing.

Question 62

Why isn't ATP a feature on pacemakers, only ICD's?

Answer 62

ATP has potential to accelerate arrhythmias into faster, more chaotic rhythms where defibrillation is the only solution. Pacemakers lack the ability to defibrillate.

Question 63

The following statement best describes which ATP pattern? 'All pacing intervals within a sequence are the same cycle length'.

Answer 63

Burst ATP.

Question 64

The following statement best describes which ATP pattern? 'Pacing intervals within a sequence feature continuously decremented cycle lengths'.

Answer 64

Ramp ATP.

Question 65

The use of advanced SVT differentiation algorithms effectively: 1. Increases sensitivity / Decreases specificity 2. Decreases sensitivity / Increases specificity

Answer 65

2 - Decreases sensitivity / Increases specificity. ## Footnote *Makes the device less sensitive to all arrhythmias but makes it more accurate at observing only the arrhythmias it needs to.*

Question 66

What is the normal shock impedance range for an ICD lead? 1. 10-99 ohm 2. 150-300 ohm 3. 500 - 1500 ohm 4. 1000 - 2000 ohm

Answer 66

1 - 10-99 ohm.

Question 67

# True or False: The following requires a high output device. 'Patient has x4 35J shocks fail to terminate VF - shocks are biphasic with alternating polarities'

Answer 67

False - safety margin is too low. High output devices max out at ~45J. ## Footnote *Implantation of a subcutaneous array would give the necessary safety margin and should be implanted.*